CA1287315C

CA1287315C - Process for the preparation of an aqueous solution of a heteropolysaccharide

Info

Publication number: CA1287315C
Application number: CA000509037A
Authority: CA
Inventors: George Van Os; Jan Jacob Bleeker; Cornelis Willem Adriaan Schram
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1985-06-06
Filing date: 1986-05-13
Publication date: 1991-08-06
Anticipated expiration: 2008-08-06
Also published as: AU592993B2; TR23766A; EP0204358A3; US4816077A; NO862226D0; EP0204358B1; GB8514315D0; EP0204358A2; OA08338A; AU5842186A; SG43893G; BR8602609A; NO172358C; NO172358B; ATE72834T1; DE3683952D1; NO862226L; US4738727A

Abstract

- ? -ABSTRACT

PROCESS FOR THE PREPARATION OF AN AQUEOUS SOLUTION
OF A HETEROPOLYSACCHARIDE

An aqueous solution of a heteropolysaccharide comprising glucose, galactose, pyruvic and succinic acid, is prepared by mixing a concentrate of said heteropolysaccharide with a saline aqueous medium containing from 12 to 30%w of at least one salt, and by shearing the mixture obtained.

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Description

~2~3~5 70474-179 The present inven-tion relates to a process for the preparation of an aqueous solution o~ a heteropolysaccharide and the use of such a solution in the production of oil from an under-grouncl oil-containiny reservoir.
The injection of wa~er to recover oil from underground oil-containiny reservoirs is well known in the art. It is also known that the use of a viscosity increasing agent in the injected water may improve the oil. recoveryO Some known viscosity-increasing agents are polyacrylamides, copolymers of acrylamides and acrylates, and polysaccharides, i.e. ~he product obtained from the cultivation of certain bacteria. Polyacrylamides show a vis-cosity loss in brines and are severely sensitive to shear. Since polysaccharides are relatively shear stable and show little vis-cosity loss in brines, they are preferred viscosity-increasing agents. They can be used in a viscosified aqueous drive fluid, hut they can also be employed in drilling fluids, well completion fluids etc.
; Generally, the polysaccharides are obtained by cultiva-tion of bacteria but the cultivation of the bacteria is not 2~ carried out at the same place as where the polysaccharide is used.
rn order to reduce transportation costs the polysaccharide is dellvered to the place where it is to be used in the form of a concentrate. The concentrate is then dlluted with any aqueous medium which ls available at this place, yieldlny a viscous aqueous solution. Aqueous media available at oil fields can be sea water, e.g. at off-shore facilities, and brin0s emanating from underground reservoirs. ~atter brines can have a very high '``' ..~i.i"

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7047~-179 salinity. From British Patent Specification No. 1,587,225 it is known that when xanthan gum, i.e. the product obtained from the cultivation of Xanthomonas bacteria, generally containing mannose, ylucose~ glucuronic acid and pyruvic acid is used as the poly-saccharide type viscosity-increasiny agent, plugging occurs in ~he underyround tests. This plugging is thought to result i.e. from precipitat.ion of polymeric salts which occurs when solutions containiny multivalent cations are injected into the reservoir.
I'his is in ayreement with the Applicant's experience that concen trates of xanthan gum when diluted with a sallne, multivalent cation-con~aining aqueous medium, yield unclear solutions which plug the filters used in filterability tests.
It has now surprisinyly been found possible ~o prepare ~rom concentrates of certain heteropolysaccharides anfl hiyhly saline aqueous media, dilute solutions having useful viscosity characteristics whilst also exhibitiny excellent filterability.
The present invention therefore provides process for the preparation of an aqueous solution of a heteropolysaccharide comprisiny glucose, galactose, pyruvic and succinic acid obtained by cultivation of a Pseudomonas bacteria or microoryanism NCIB
11883, or mutants thereof, in which process a concentrate of said heteropolysaccharide is mixed with a saline aqueous medium con~aining ~rom 12 to 30%w of at least one salt selected from alkali metal salts and alkaline earth metal salts, and the mixture obtained is sheared at a temperature ranying from 20 to 100C, at a pressure in the range 1 x 105 to 15 x 105Pa, at a shear rate from 10,000 to 200,000 s 1 and at a power input of 0.5 to 10 ,~ . ., - ,. , :' .

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3 ~L r5 7~74-179 }~Wh/m3. The percentages are based on the total of water and salt(s).
Suitable heteropolysaccharides comprise glucose and for each 7 moles of glucose 0.9-1.2 moles of galactose and 0.65 to 1.1 moles of pyruvic acid and up to 2 moles of succinic acid, optionally in combination with acetic acid. Preferably the heteropolysaccharides are obtained from cultivation of Pseudomonas-type bacteria, in particular P eudomonas sp. NCIB
11264 (e.y. as described in United Kingdom Patent SpeciEication No. 1,539,064), Pseudomonas sp. NCIB 11592 (e.g. as described in Canadian Patent No. 1,173,771) or microorganism NCIB 11883) e.g.
as described in 2a .

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EP-~-138 255) or mutants thereof. However, cultivation products of other bacteria, such as Rhizebium or Agrobacterium bacteria, are suitable as well.
The feedstock of the present process is a concentrate.
~his concentrate is usually such that it can be poured into and out of drums m which it is transported to the oil fields. The heteropolysaccharide concentrate is preferably an aqueous concentrate containing 4 to 15~w of said heteropolysaccharide.
m ese concentrations ensure that on the one hand the feedstock o is sufficiently concentrated to avoid unnecessary transportation costs whereas on the other hand it is readily dilutable in an aqueous mediumO
Brine or sea water when used as saline aqueous medium with which the concentrate is diluted, generally contains several salts. Usually aIkali metal salts, such as sodium and pot~assium salts are present, together with alkaline earth metal salts such as calcium and magnesium salts. The aqueous medium may further contain munor amounts of other polyvalent metal ions as will be recognised by a person skilled in the art. me pH of the saline ?~ aqueous medium is not critical. Both acidic and alkaline media may be employed.
The preparation of the diluted heteropolysaccharide solution can be carried out batchwise. Ihereto, a concentrate is fed into a tank, the saline aqueous medium is fed therein, too, in t~e required quantity, and with a mLxing device the admixture is mlxed under shearing. Preferably, the concentrate and the saline aqueous medium are mixed and sheared in a continuous manner. ~hereto, the concentrate and the saline aqueous medium are intrc~uced into an Ln line wet comminution 3o machine. In such a machine a great amount o~ energy is imparted to the concentrate and the aqueous medium through forces of impact and hydraulic shear. Such machLnes usually cGmprise a rotor and a stator. The degree of particle breakdown can be controlled by regulating the gap between the rotor and the BKOl.009 '' , stator which are present in such comminution machines. The presen~ invention is not limited to any type of comminution machines. Many types, includin~ machines for batch processes, can be used in the present process. As stated above the concentrate and saline aqueous medium are mixed and sheared at a temperature ranginy from 20 to 100C, at a pressure in the range 1 x 105 to 15 x 105Pa, at a shear rate of 10,000 to 200,000 s 1 and at a power input of 0.5 to 10 kWh/m3.
The extent of dilution can be set at any desired level.
The concentration of the solution is generally selected in dependency on the desired viscosit~. Preferably, the viscosity of the solution obtained after shearing ranges from 2 to 400 mPa.s, in paxkicular from 5 to 100 mPa.s ~at a shearing rate of 7.5 s 1 and at 30 C). The solution suitably contains from 100 to 2000 ppmw of heteropolysaccharide. The present process will be elucidated by means of the following examples.
EXAMPLES
Two heteropolysaccharides were tested, heteropoly-saccharide I heing a 7.7%w concentrate of a Pseudomonas NCIB 11592 heteropolysaccharide (as described in Canadian Patent No.
1,173,771) containing glucose, galactose, pyruvic acid and succini~ acid, and heteropolysaccharide II being a 7.~w xanthan gum concentrate derived from Xanthomonas campestris NCIB lla54 (as described ln Canadian Patent No. 1,223,224). These concentrates were mixed with one of two brines, brine A comprising 15%w of NaCl and 1.5%w o~ CaCl~ in water, and brine B comprising 25%w of NaCl 2.5%w of CaCl~ and 2%w of MgC12 in water, the weight percentacJes .

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73~5 being based on the total of salts ancl water.
EX~MPLE I
A series of tests were run using a colloid mill with a slit width of 0.008 ft (2.44 mm), at a shearing rate of 100,000 s , a throughout of 0.23 l/s and a power inpu~ of 1.86 kWh/m3 per pass through the colloid mill. The conc~entrates were mixed with the amount of brine to achieve a suitable ~oncentration for the mixture and passed 5 times through the colloid mil. After the . 4a '''''~., ~. .

~2~3~5i second and following passes the filterability (Fi) and viscosit~ of the muxture were determined. The filterability is expressed as the time in seconds in which a litre of the solution is passed through a 1.2~m filter at 40 psig (2.44 x 105Pa) pressure difference and at 30C. me viscosity is measured at 30C and at a shearing rate of 7~5 s 1.
Results of the tests are shcwn in Table I.

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TABLE I
Heteropoly Brine Concentration Pass Fi ~ Power saccharide ppmw s input mPa.s kWh/m~
A 375 2 113 21.7 3.72 3 93 2106 5.58 4 101 21.7 7.44 5 92 21.7 9.30 I B 250 2 244 10.2 3.72 3 212 10.3 5.58 4 198 lO.~ 7.44 iC~ 5 203 10.3 9.30 II A 400 2blockmg _ 5.58 5 ll 19.6 9.30 ~,~II B 250 24blocking _ 5 58 5 ~ l~ - 9.8 9.30 ~XAMPLE II
,~v A seoond series of ~ eriments were run using a static hi~h ,q~ ~ shear mixer (Ultra torrax TP 45/4 G). A concentrate and a brine were mixed and subjected to shear at a shearing rate of 100,000 s 1 for a number of seconds. Periodically the filterability and viscosity, as defined in Example I, were determined. The experimental data are indicated in Table II.

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73~3 EXAMPLE III
In an experiment brine B and concentrate of heteropolysaccharide I were~supplied to an in line wet ccmminution machine ~Dispax 3-6/6) in such quantities that the resulting mixture contained 250 ppmw of heteropolysaccharide.
The machine was operated at a sh OE ing rate of 43,000 s l, a throughpu~ of 1.6 m3/h and a power input of 1.18 KWh/m3. After one pass the filterability of the solution was 75 s/l and the viscosity was 11.0 mæa.s at 7.5 s 1 and 30C.
1~J From the above Examples it is apparent that xanthan gum can hardly be dissolved in high salinity brines and no useful product is obtained thereby, whereas heteropolysaccharide I can easily be dissolved at a power input below 10 kWh/m3 yielding solutions with excellent filterability and viscosity properties.
~,r` Use of an m line wet oomninution machine yields effective solutions at the lowest power input.

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Claims

1. Process for the preparation of an aqueous solution of a heteropolysaccharide comprising glucose, galactose, pyruvic and succinic acid obtained by cultivation of a Pseudomonas bacteria or microorganism NCIB 11883, or mutants thereof, in which process a concentrate of said heteropolysaccharide is mixed with a saline aqueous medium containing from 12 to 30%w of at least one salt selected from alkali metal salts and alkaline earth metal salts, and the mixture obtained is sheared at a temperature ranging from 20 to 100°C, at a pressure in the range 1 x 105 to 15 x 105Pa, at a shear rate from 10,000 to 200,000 s-1 and at a power input of 0.5 to 10 kWh/m3.

2. Process according to claim 1, in which the heteropoly-saccharide is obtained by cultivation of Pseudomonas sp. NCIB
11264 or Pseudomonas sp. NCIB 11592, or mutants thereof.

3. Process according to claim 1, in which the heteropoly-saccharide concentrated is an aqueous concentrate containing 4 to 15%w of said heteropolysaccharide.

4. Process according to claim 2, in which the heteropoly-saccharide concentrated is an aqueous concentrate containing 4 to 15%w of said heteropolysaccharide.

5. Process according to any one of claims 1 to 4, in which the concentrate and the saline aqueous medium are mixed and sheared in continuous manner.

6. Process according to any one of claims 1 to 4, in which the viscosity of the solution obtained after shearing ranges from 2 to 400 mPa.s at a shear rate of 7.5 s-1 and at 30°C.

7. Process according to any one of claims 1 to 4, in which the concentrate and the saline aqueous medium are mixed and sheared in continuous manner and the viscosity of the solution obtained after shearing ranges from 2 to 400 mPa.s at a shear rate of 7.5 s-1 and at 30°C.

8. Process according to any one of claims 1 to 4, in which the solution contains from 100 to 2000 ppmw of heteropoly-saccharide.

9. Process according to any one of claims 1 to 4, in which the viscosity of the solution obtained after shearing ranges from 2 to 400 mPa.s at a shear rate of 7.5 s-1 and at 30°C and the solution contains from 100 to 2000 ppmw of heteropolysaccharide.

10. Process for the extraction of oil from an underground oil-containing reservoir which comprises injecting into said reservoir an aqueous solution of a heteropolysaccharide prepared by a process according to any one of claims 1 to 4.

11. Process for the extraction of oil from an underground oil-containing reservoir which comprises injecting into said reservoir an aqueous solution of a heteropolysaccharide prepared by a process according to claim 9.